Underactive Thyroid

1. Introduction

  • Definition: Hypothyroidism, or underactive thyroid, is a condition where the thyroid gland fails to produce sufficient thyroid hormones (T3 and T4) to meet the body’s metabolic needs.
  • Epidemiology: Hypothyroidism affects approximately 5% of the population globally, with higher prevalence in women and older adults.
  • Significance: Untreated hypothyroidism can lead to severe complications like myxoedema coma and long-term cardiovascular disease.

2. Causes and Risk Factors

  • Causes:
    • Primary Hypothyroidism (most common):
      • Hashimoto’s thyroiditis (autoimmune destruction of the thyroid gland).
      • Iodine deficiency or excess.
      • Thyroid surgery or radioiodine therapy.
    • Secondary Hypothyroidism:
      • Pituitary or hypothalamic dysfunction, leading to inadequate TSH or TRH production.
  • Risk Factors:
    • Female sex, age >50 years.
    • Family history of thyroid disorders or autoimmune diseases.
    • Previous radiation exposure or neck surgery.

3. Pathophysiology

  • Insufficient thyroid hormone production disrupts metabolic homeostasis. The pituitary gland compensates by increasing TSH secretion in primary hypothyroidism. Reduced thyroid hormone levels lead to slowed metabolic processes, causing characteristic symptoms like fatigue, weight gain, and cold intolerance.

4. Symptoms and Features

  • General Symptoms:
    • Fatigue, weight gain, and cold intolerance.
    • Dry skin, hair thinning, and brittle nails.
    • Constipation and hoarseness.
  • Specific Features:
    • Puffy face, periorbital swelling.
    • Slow heart rate (bradycardia).
    • Depression or cognitive impairment (“brain fog”).
    • Menstrual irregularities (e.g., heavy or irregular periods).

5. Complications

  • Myxoedema coma: A life-threatening complication characterised by hypothermia, bradycardia, and altered mental status.
  • Cardiovascular disease: Increased risk due to hyperlipidaemia.
  • Infertility or pregnancy complications (e.g., miscarriage, preeclampsia).
  • Goitre: Thyroid gland enlargement due to chronic TSH stimulation.

6. Diagnosis

  • Clinical Features: Symptoms like fatigue, weight gain, and cold intolerance raise suspicion.
  • Laboratory Tests:
    • TSH: Elevated in primary hypothyroidism (>4.0 mIU/L).
    • Free T4: Low levels confirm hypothyroidism.
    • Thyroid antibodies (anti-TPO, anti-thyroglobulin): Positive in autoimmune thyroiditis.
  • Imaging: Thyroid ultrasound or radioactive iodine uptake scan for structural or functional abnormalities.

7. Management Overview

  • Goals: Normalise thyroid hormone levels, alleviate symptoms, and prevent complications.
  • Approach: Lifelong thyroid hormone replacement therapy, regular monitoring, and lifestyle modifications.

8. Treatment Options with Cost (USD)

  • Thyroid Hormone Replacement:
    • Levothyroxine (T4): ~$10–$30 per month.
    • Liothyronine (T3): ~$20–$50 per month (used less commonly).
  • Adjunctive Therapies:
    • Selenium supplements: ~$10–$20 per bottle (for autoimmune thyroiditis).

9. Advanced Treatment Options with Cost (USD)

  • Combination Therapy: T4 + T3 for refractory symptoms despite normal TSH (cost: ~$40–$70/month).
  • Surgery: Rarely needed unless goitre causes compressive symptoms (~$10,000–$15,000).

10. Pharmacological Treatment

  • First-line: Levothyroxine is the standard treatment for hypothyroidism.
  • Alternative: Liothyronine (T3) or desiccated thyroid extract for select patients with persistent symptoms despite levothyroxine therapy.

11. Medication Tables

Table 1: Doses and Side Effects

DrugIndicationDoseCommon Side Effects
LevothyroxineHypothyroidism1.6 mcg/kg/day (adjust as needed)Overdose: palpitations, anxiety
LiothyroninePersistent symptoms on T425 mcg/day (adjust as needed)Palpitations, insomnia
SeleniumAutoimmune thyroiditis100–200 mcg/dayNausea, metallic taste

Table 2: Brand Names and Approximate Costs (USD)

DrugBrand NamesApprox. Cost
LevothyroxineSynthroid, Euthyrox$10–$30 per month
LiothyronineCytomel$20–$50 per month
SeleniumSelenase$10–$20 per bottle

12. Lifestyle Interventions

  • Maintain a healthy, balanced diet rich in iodine (e.g., iodised salt, seafood) and selenium.
  • Avoid excessive intake of goitrogens (e.g., raw cruciferous vegetables).
  • Exercise regularly to combat fatigue and weight gain.
  • Ensure adherence to medication, taking levothyroxine on an empty stomach for optimal absorption.

13. Monitoring Parameters

  • Regular TSH and free T4 levels every 6–8 weeks after initiating or adjusting therapy, then annually once stable.
  • Monitor for symptom resolution, including fatigue, weight changes, and cognitive function.
  • Screen for potential side effects of overtreatment (e.g., hyperthyroidism symptoms).

14. Patient Counseling Points

  • Educate about the lifelong nature of thyroid hormone replacement and the importance of adherence.
  • Instruct on taking levothyroxine at the same time daily, preferably in the morning on an empty stomach.
  • Discuss potential drug interactions, such as with calcium or iron supplements, which can impair absorption.
  • Highlight the importance of routine monitoring to ensure proper dosing.

15. Special Populations

  • In Pregnancy: Thyroid hormone requirements increase; closely monitor and adjust levothyroxine dose to maintain TSH <2.5 mIU/L.
  • In Elderly: Start at a lower dose (e.g., 25–50 mcg/day) to reduce the risk of cardiac side effects.
  • In Children: Weight-based dosing is essential; monitor growth and development.

16. Prevention

  • Iodine supplementation in iodine-deficient regions to prevent primary hypothyroidism.
  • Routine thyroid function screening in high-risk individuals (e.g., pregnant women, those with autoimmune diseases).
  • Avoid excessive iodine intake from supplements or diet.

17. FAQs

  1. What is hypothyroidism?
    Answer: A condition where the thyroid gland doesn’t produce enough thyroid hormones, slowing metabolism.
  2. What causes hypothyroidism?
    Answer: Common causes include autoimmune thyroiditis, iodine deficiency, and thyroid surgery.
  3. How is hypothyroidism treated?
    Answer: With levothyroxine, a synthetic thyroid hormone.
  4. Is hypothyroidism curable?
    Answer: It’s usually a lifelong condition, but symptoms can be managed effectively with treatment.
  5. How is hypothyroidism diagnosed?
    Answer: By measuring TSH (elevated in primary hypothyroidism) and free T4 (low).
  6. What foods help with hypothyroidism?
    Answer: Iodine-rich foods like seafood and selenium-rich foods like nuts.
  7. What are the symptoms of hypothyroidism?
    Answer: Fatigue, weight gain, dry skin, hair thinning, and cold intolerance.
  8. Can hypothyroidism cause weight gain?
    Answer: Yes, due to slowed metabolism.
  9. How often should thyroid levels be checked?
    Answer: Every 6–8 weeks after starting or adjusting therapy, then annually.
  10. Can hypothyroidism affect pregnancy?
    Answer: Yes, it increases the risk of complications; proper treatment is essential.
  11. Can hypothyroidism cause depression?
    Answer: Yes, it can contribute to low mood and cognitive impairment.
  12. Is levothyroxine safe?
    Answer: Yes, when taken at the correct dose under medical supervision.
  13. Can hypothyroidism cause hair loss?
    Answer: Yes, but hair usually regrows with proper treatment.
  14. What is myxoedema?
    Answer: A severe form of hypothyroidism causing swelling, lethargy, and potentially life-threatening symptoms.
  15. Can hypothyroidism be prevented?
    Answer: Iodine deficiency can be prevented with adequate iodine intake.